As our understanding of the nervous system increases, the questions posed by neuroscientists become more complex and require more sophisticated analytical schemes to answer them.. A major challenge of contemporary neurobiology is to understand the cellular mechanisms responsible for neurotransmitter targeting and release. Essential to an understanding of neurotransmitter release is quantitative knowledge of the amounts and locations of neuropeptides present in the neuron. The methods currently employed for the assay of small molecules are not sensitive enough to quantitate the neuropeptides found within small subsections of individual neurons nor to detect the release of neurotransmitters from a single electrical stimulation. The long term objective of this research program is develop and demonstrate new analytical instrumentation and methodology to allow the identification and quantitation of neuronal releasates from a single nerve terminal, and measurement of the contents of individual varicosities along a single nerve process. The approach used to accomplish these goals is capillary electrophoresis followed by radiochemical detection. Once the instrumentation and methodology is in place, individual cultured neurons of the giant marine mollusk Aplysia californica will be studied. These studies will answer the questions: do the neurons target different neuropeptides to specific release sites, and can the neuron release different neuropeptides at specific terminals? By using the latest advances in separation science and detector technology, significant gains can be made in our understanding of the differential packing, distribution, and release of neurotransmitters in Aplysia. In leading to a description of the subcellular dynamics of neuronal signalling, this work will contribute to the basic understanding of the nervous system. The symptoms of many mental disorders suggest that an imbalance of chemical messengers may be responsible for the disease state. By answering questions of neurotransmitter targeting and release, we will gain further insight into how complex systems of neurons interact in both healthy and diseased systems.